1. Field of the Invention
This invention pertains to an oil recovery method, and more particularly to a thermal oil recovery method in which a second permeable oil formation having a temperature higher than the temperature of the first viscous oil-containing formation is utilized to heat water and dissolve hydrocarbons from the deep formation which mixture of water and hydrocarbons is then injected into the viscous oil formation to displace and decrease the viscosity of the viscous oil contained in the viscous oil formation.
2. Description of the Prior Art
There are many subterranean, viscous petroleum-containing formations for which little or no petroleum can be recovered even though the formation permeability is adequate for ordinary oil recovery operations, because the petroleum at formation conditions is so viscous that substantially no movement of petroleum occurs even if a pressure differential is applied across the formation. That is to say, even in primary recovery operations in which natural energy existing in the formation is utilized for oil recovery, such as bottom water drive or solution gas drive, etc. or by application of enhanced recovery methods in which an artificial energy drive is applied to the formation, such as by water flooding, only a small fraction or even none of the oil present in the formation can be recovered. In order to permit recovery of viscous petroleums from such formations, some treatment must be employed to decrease the viscosity of the petroleum to a value at which it will move through the permeable formation.
For the purpose of the present application, we mean by the term "visous petroleum," any formation petroleum having an API gravity less than about 25.degree. API, which corresponds to a viscosity at standard conditions of about 30 centipoise at 100.degree. F.
Thermal recovery methods have been utilized in the past and there are many discussions thereof in the literature. Steam flooding has been especially successful in recovering viscous petroleum from many viscous petroleum-containing formations. Hot water flooding has also been used successfully for such purposes.
In the past, a commercially successful recovery operation required that there be available in the vicinity of the field from which petroleum is being recovered, an inexpensive source of fuel such as natural gas or other hydrocarbon fuels. Because of the recently developed shortage of natural gas and other hydrocarbon fuels, it has become increasingly difficult to locate a source of fuel to heat the water or other fluid for thermal recovery operations.
In view of the foregoing discussion and the present critical energy shortage, it can be appreciated that there is a substantial need for a method of recovering viscous petroleum from subterranean, viscous petroleum-containing formations which do not require the burning of extraneous fuels on the surface of the earth for the purpose of generating the steam or other heated fluid to be injected into the oil formation.